1、UL COPYRIGHTED MATERIAL NOT AUTHORIZED FOR FURTHER REPRODUCTION ORDISTRIBUTION WITHOUT PERMISSION FROM ULUNDERWRITERS LABORATORIES CERTIFICATION REQUIREMENT DECISIONThis Certification Requirement Decision is prepared and published by Underwriters Laboratories (UL). Itis normative for the applicable
2、UL Product Certification Program(s); however, it is currently not part ofthe UL Standard(s) referenced below.Product Category (CCN): SHZZ, SHMRStandard Number: UL 250Edition Date: November 1, 1993Edition Number: 10Section / Paragraph Reference: 5.8.9 DEFROST CONTROL NEUTRALDECISION:Revise Standard a
3、s follows:5.8.9 A switch acting as a safety control, such as a temperature-limiting control or an overcurrentprotecting device of the single-pole type, shall be electrically connected to the ungrounded conductor ofthe supply circuit.Exception: The defrost temperature limiting control is capable of b
4、eing electrically located in the neutralconductor if there is an additional time or temperature operated control in the ungrounded conductor. Therefrigerator shall comply with the requirements of the defrost heater burnout test (Clause 8.10) with thetemperature limiting control shorted, so that only
5、 the additional control is used to terminate the defrostcycle.RATIONALE FOR DECISION:Clause 5.8.9 currently requires the defrost temperature limiting control to be electrically connected to theungrounded conductor. Since the defrost timer is usually also connected to the ungrounded conductor,this le
6、aves the neutral side of the heater unprotected. This is undesirable, especially if refrigerators canbe exposed to reverse polarity. In this case, it is better to put the limiting control and timer on oppositesides of the defrost heater. Reviewing this construction from a single-fault standpoint, th
7、e constructionis acceptable as long as a control is provided in each leg of the circuit and the unit passes the burnouttest with each control shorted in turn. The use of the temperature limiting control in the neutral providesprotection against a shorted defrost heater on a reversed polarity circuit
8、.Copyright 2007 Underwriters Laboratories Inc.UL, in performing its functions in accordance with its objectives, does not guarantee or warrant thecorrectness of Certification Requirement Decisions it may issue or that they will be recognized or adoptedby anyone. Certification Requirement Decisions a
9、re the opinion of Underwriters Laboratories Inc. inpractically applying the requirements of the standard. They do not represent formal interpretations of thestandard under American National Standards Institute (ANSI) processes. UL shall not be responsible toanyone for the use of or reliance upon Cer
10、tification Requirement Decisions by anyone. UL shall not incurany obligation or liability for damages, including consequential damages, arising out of or in connectionwith the use or reliance upon Certification Requirement Decisions. The electronic version of theCertification Requirement Decision is the current version and previously printed copies may be outdated.This document is published as a service to ULs certification customersUL COPYRIGHTED MATERIAL NOT AUTHORIZED FOR FURTHER REPRODUCTION ORDISTRIBUTION WITHOUT PERMISSION FROM ULSTANDARD NUMBER: UL 250 -2-No Text on This Page
